1. Field of the Invention
This invention relates generally to the field of wireless communications and more specifically to transmit diversity devices.
2. Description of the Related Art
Transmitting devices using a plurality of antennae to transmit a signal simultaneously using a diversity parameter may reduce the total transmission power required for a signal to reach a receiving communication device when compared to using one antenna only. Multiple antenna elements in the transmitting device may enhance spectral efficiency and capacity, while reducing signal degradation caused by multi-path and fading. One or more transmit diversity parameter may be applied to signals transmitted from two or more antennae, and may modify an effective power distribution detected by receiving communication devices, such as base stations. The transmitted signals may propagate along different paths and may reach the receiving communication device with different phases that may interfere. The total power of the interfering signals perceived by base stations may change with varying parameters of transmit diversity control. It is a goal of mobile transmit diversity devices to minimize destructive interference of signals at the base station in order to increase the total power of the received signals.
US Patent Publication No. 2008/0227404, entitled “Method, Apparatus, and System for Providing Feedback to Transmit Diversity Device”, published Sep. 18, 2008 and assigned to the assignee of the present application, the contents of which are incorporated herein by reference, describes optimizing transmit diversity parameters to reduce destructive interference of signals from different antennae received at the base station. One such method includes matching the wavepatterns of the signals from different antennae so that the signals coincide and constructively interfere.
However, with this solution, a new problem is encountered. In a wireless connection, for a base station to receive transmitted signals, the base station may require that the signals reach the base station with a power greater than a predetermined threshold. Diversity gain is a measure of the reduction in the total transmission power of the transmit diversity device by using two or more antennae compared using one antenna in order to meet the required predetermined threshold of power at the base station. When the wavepatterns of signals from different antennae coincide, a maximum power region of a signal from one antenna may be added to a corresponding maximum power region of a signal from another antenna. The result is a large diversity gain at maximum power regions of the waveform of the signals. However, a receiving base station may be located outside of a maximum power region, in minimum power regions of the waveform of the signals.
There is a need for a system, device, and method, to improve the diversity gain of transmit diversity devices.